Refactor lfsr_digest16

include/util.h

@@ -151,12 +151,12 @@ uint8_t lfsr_digest8_reflect(uint8_t const message[], int bytes, uint8_t gen, ui
 
 /// Digest-16 by "LFSR-based Toeplitz hash".
 ///
-/// @param data up to 32 bits data, LSB aligned
-/// @param bits number of bits to digest
+/// @param message bytes of message data
+/// @param bytes number of bytes to digest
 /// @param gen key stream generator, needs to includes the MSB if the LFSR is rolling
 /// @param key initial key
 /// @return digest value
-uint16_t lfsr_digest16(uint32_t data, int bits, uint16_t gen, uint16_t key);
+uint16_t lfsr_digest16(uint8_t const message[], unsigned bytes, uint16_t gen, uint16_t key);
 
 /// Compute bit parity of a single byte (8 bits).
 ///

src/devices/maverick_et73x.c

@@ -80,15 +80,15 @@ static int maverick_et73x_callback(r_device *decoder, bitbuffer_t *bitbuffer)
     else if (flags == 7)
         status = "init";
 
-    //bitbuffer_extract_bytes(bitbuffer, row, 12, b, 24);
-    uint32_t chk_data = (b[1] & 0x0f) << 20 | b[2] << 12 | b[3] << 4 | b[4] >> 4;
+    uint8_t chk[3];
+    bitbuffer_extract_bytes(&mc, 0, 12, chk, 24);
 
     //digest is used to represent a session. This means, we get a new id if a reset or battery exchange is done.
-    int id = lfsr_digest16(chk_data, 24, 0x8810, 0xdd38) ^ digest;
+    int id = lfsr_digest16(chk, 3, 0x8810, 0xdd38) ^ digest;
 
     if (decoder->verbose)
-        fprintf(stderr, "%s: pre %03x, flags %0x, t1 %d, t2 %d, digest %04x, chk_data %06x, digest xor'ed: %04x\n",
-                __func__, pre, flags, temp1, temp2, digest, chk_data, id);
+        fprintf(stderr, "%s: pre %03x, flags %0x, t1 %d, t2 %d, digest %04x, chk_data %02x%02x%02x, digest xor'ed: %04x\n",
+                __func__, pre, flags, temp1, temp2, digest, chk[0], chk[1], chk[2], id);
 
     data = data_make(
             "model",            "",                     DATA_STRING, "Maverick-ET73x",

src/devices/tfa_30_3196.c

@@ -76,9 +76,8 @@ static int tfa_303196_callback(r_device *decoder, bitbuffer_t *bitbuffer)
     if (b[0] != 0xa8)
         return DECODE_FAIL_SANITY;
 
-    uint32_t chk_data = ((unsigned)b[0] << 24) | (b[1] << 16) | (b[2] << 8) | (b[3]);
     uint16_t digest   = (b[4] << 8) | (b[5]);
-    int chk           = lfsr_digest16(chk_data, 32, 0x8810, 0x22d0) ^ digest;
+    int chk           = lfsr_digest16(b, 4, 0x8810, 0x22d0) ^ digest;
 
     //bitrow_printf(b, 48, "TFA-303196 (%08x  %04x  %04x): ", chk_data, digest, session);
 

src/util.c

@@ -256,21 +256,24 @@ uint8_t lfsr_digest8_reflect(uint8_t const message[], int bytes, uint8_t gen, ui
     return sum;
 }
 
-uint16_t lfsr_digest16(uint32_t data, int bits, uint16_t gen, uint16_t key)
+uint16_t lfsr_digest16(uint8_t const message[], unsigned bytes, uint16_t gen, uint16_t key)
 {
     uint16_t sum = 0;
-    for (int bit = bits - 1; bit >= 0; --bit) {
-        // fprintf(stderr, "key at bit %d : %04x\n", bit, key);
-        // if data bit is set then xor with key
-        if ((data >> bit) & 1)
-            sum ^= key;
+    for (unsigned k = 0; k < bytes; ++k) {
+        uint8_t data = message[k];
+        for (int i = 7; i >= 0; --i) {
+            // fprintf(stderr, "key at bit %d : %04x\n", i, key);
+            // if data bit is set then xor with key
+            if ((data >> i) & 1)
+                sum ^= key;
 
-        // roll the key right (actually the lsb is dropped here)
-        // and apply the gen (needs to include the dropped lsb as msb)
-        if (key & 1)
-            key = (key >> 1) ^ gen;
-        else
-            key = (key >> 1);
+            // roll the key right (actually the lsb is dropped here)
+            // and apply the gen (needs to include the dropped lsb as msb)
+            if (key & 1)
+                key = (key >> 1) ^ gen;
+            else
+                key = (key >> 1);
+        }
     }
     return sum;
 }